True or false: (a) The C¬C bonds in benzene are all the same length and correspond to typical single C¬C bond lengths. (b) The C¬C bond in acetylene, HC≡CH, is longer than the average C¬C bond length in benzene.

Verified step by step guidance

Step 1: Understand the structure of benzene. Benzene (C₆H₆) is a cyclic hydrocarbon with alternating double and single bonds, often represented as a hexagon with a circle inside, indicating resonance. This resonance leads to equal bond lengths between all carbon atoms.

Step 2: Compare the bond lengths in benzene. Due to resonance, the C-C bonds in benzene are intermediate between a single bond (approximately 1.54 Å) and a double bond (approximately 1.34 Å), resulting in a bond length of about 1.39 Å, which is shorter than a typical single C-C bond.

Step 3: Analyze the structure of acetylene. Acetylene (HC≡CH) contains a carbon-carbon triple bond. Triple bonds are shorter than both single and double bonds, with a typical length of about 1.20 Å.

Step 4: Compare the bond lengths in acetylene and benzene. The C-C bond in acetylene is a triple bond, which is shorter than the average C-C bond length in benzene (1.39 Å).

Step 5: Evaluate the statements. (a) False: The C-C bonds in benzene are not typical single bond lengths due to resonance. (b) False: The C-C bond in acetylene is shorter, not longer, than the average C-C bond length in benzene.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Resonance in Benzene

Benzene is a cyclic compound with a structure that exhibits resonance, meaning that its electrons are delocalized across the carbon atoms. This results in all C-C bonds in benzene being of equal length, which is intermediate between a typical single bond and a double bond. Therefore, the statement about the C-C bonds in benzene being the same length is true.

Bond Lengths and Types

Bond length is influenced by the type of bond between atoms. A single bond (C-C) is generally longer than a double bond (C=C), and a triple bond (C≡C) is the shortest. In this context, the bond length in acetylene (HC≡CH) is shorter than that in benzene due to the presence of a triple bond, making the statement about acetylene's bond length being longer than that in benzene false.

Comparative Bond Lengths

Understanding comparative bond lengths is crucial in organic chemistry. The average C-C bond length in benzene is approximately 1.39 Å, while the C-C bond length in acetylene is about 1.20 Å. This difference highlights how bond order affects bond length, with higher bond orders resulting in shorter bonds, thus reinforcing the false nature of the second statement.

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Average Bond Order

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Textbook Question

Mothballs are composed of naphthalene, C₁₀H₈, a molecule that consists of two six-membered rings of carbon fused along an edge, as shown in this incomplete Lewis structure:(a) Draw all of the resonance structures of naphthalene. How many are there?

Textbook Question

Mothballs are composed of naphthalene, C₁₀H₈, a molecule that consists of two six-membered rings of carbon fused along an edge, as shown in this incomplete Lewis structure:

(b) Do you expect the C—C bond lengths in the molecule to be similar to those of C—C single bonds, C ═C double bonds, or intermediate between C—C single and C ═C double bonds?

Textbook Question

Mothballs are composed of naphthalene, C₁₀H₈, a molecule that consists of two six-membered rings of carbon fused along an edge, as shown in this incomplete Lewis structure:

(c) Not all of the C—C bond lengths in naphthalene are equivalent. Based on your resonance structures, how many C—C bonds in the molecule do you expect to be shorter than the others?